docs: update README for 418 languages and dev setup

Update description, test counts, and setup instructions to reflect
expanded language support. Add requirements-dev.txt to setup steps.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -8,12 +8,12 @@ sdk_version: 6.8.0
 app_file: app.py
 pinned: false
 license: apache-2.0
-short_description: Translate English text to 22 production-ready languages.
+short_description: Translate between 418 languages.
 ---
 
 # MADLAD-400 Translate
 
-Translate English text to 22 production-ready languages (BLEU 35+ both directions, Section A.10) using Google's [MADLAD-400](https://arxiv.org/pdf/2309.04662) 3B model.
+Translate between 418 languages from Table 9 (Section A.1) of Google's [MADLAD-400](https://arxiv.org/pdf/2309.04662) 3B model.
 
 ## Requirements
 
@@ -27,6 +27,7 @@ Translate English text to 22 production-ready languages (BLEU 35+ both direction
 uv venv --python 3.12
 source .venv/bin/activate
 uv pip install -r requirements.txt
+uv pip install -r requirements-dev.txt   # dev tools
 python app.py
 ```
 
@@ -38,6 +39,6 @@ The Gradio interface launches at `http://localhost:7860`.
 ruff check .             # lint
 ruff format .            # format
 ty check                 # type check
-pytest -m "not slow"     # 33 fast tests
-pytest                   # all 43 tests (slow require CUDA + model download)
+pytest -m "not slow"     # 38 fast tests
+pytest                   # all 48 tests (slow require CUDA + model download)
 ```